Fatty acyl isethionates (e.g., cocoyl isethionates) are anionic surfactants highly desirable in personal care skin or hair cleansing products, particularly in personal care products, because they lather well, are mild to the skin and have good emollient properties. Typically, fatty acid isethionates are produced by esterification of fatty acids or by reaction of fatty acid chloride having carbon chain length of C8 to C20 with isethionate. A typical surfactant product (e.g., commercially sold or made surfactant product) containing fatty acyl isethionate contains about 40 to 95 wt. % fatty acyl isethionate, and 0 to 50 wt. %, typically 5 to 40 wt. % free fatty acid, in addition to isethionate salts, typically at less than 5%, and trace (less than 2 wt. %) of other impurities.
A problem with the ready use of commercially sold or made fatty acyl isethionate product in liquid compositions, wherein the acyl isethionate surfactant product is used as a primary surfactant comprising a level of at least 60% wt % of total fatty isethionate surfactant product and other synthetic surfactants in the liquid composition, however, is the low solubility of these compounds in water. This is especially true for fatty acyl isethionate surfactant product containing high level of free fatty acid/fatty soaps (10% by wt. or higher) and/or long chain fatty acyl isethionates component (e.g., C14 and higher). The fatty acyl isethionate component of the surfactant product tends to form insoluble surfactant crystals with the amount of crystals depending strongly on the storage temperature due to the wide range of dissolution temperatures of these crystals. This in turn results in unstable liquid cleansers which exhibit very thick or very thin consistency at low and elevated temperatures. At low temperature, the liquid composition becomes a semi-solid gel which is difficult to use. At elevated temperature, the liquid composition turns into water-thin liquid which causes phase separation of the product.
It would therefore be of tremendous advantage to have compositions having consistent viscosity at both low and elevated temperatures; as well as a way of manipulating compositional ingredients to ensure such consistent viscosity is obtained and that fatty acyl isethionate product, no matter what their free fatty acid/fatty soap content or what the chain lengths of the fatty acyl isethionate, fatty acid or fatty acid soap component, can be readily used as the primary surfactant (comprising at least 60% of total surfactants) in a liquid cleanser composition. The present invention provides precisely such compositions and processes for making such compositions.
Specifically, the invention recognizes that the problem of inconsistent viscosity and physical instability can be resolved by converting part of the fatty acyl isethionate and fatty acid crystals to viscous surfactant liquid crystals at a temperature at or above the dissolution temperature of these long chain fatty acid and/or fatty acyl isethionate crystals such that the liquid composition in which the surfactant product will be used has a high enough viscosity to ensure stability, said stability being defined by the absence of visible physical separation after two weeks of storage at 45° C. This is accomplished by using an elevated temperature storage stabilizing system in the composition comprising a combination of (1) alkanolamide and/or alkylamineoxide and (2) an ingredient selected from the group consisting of ammonium salt, hydrocarbon oils, organic amine, fatty alcohol, fatty acid and mixture of the above ingredients. The compounds of the stability system are believed to modify the surfactant crystal and creates a more consistent viscosity which allows fatty acyl isethionate product, regardless of free fatty acid content or the chain length of isethionates, fatty acids, and/or fatty acid soaps to have more consistent viscosity at both low and elevated temperatures and to thereby be storage stable.
Acyl isethionate liquids do exist in the art. U.S. Pat. No. 5,415,810 to Lee et al., for example, discloses compositions comprising fatty acyl isethionates and zwitterionic surfactant (e.g., cocoamidopropyl betaines), presumably to help solubilize the isethionate and make an isotropic liquid. The reference separately teaches away from use of both alkanolamides (column 1, lines 27-30), and use of free fatty acids, especially longer chain fatty acids (column 2, lines 34-39), let alone the use of both specifically in combination.
U.S. Pat. No. 5,739,365 to Brody et al. and U.S. Publication No. 2004/0224863 both disclose use of synthetic surfactants having ammonium counterion to help solubilize fatty acid isethionate.
U.S. Pat. No. 5,132,037 to Greene et al. (and related U.S. Pat. No. 5,234,619 and U.S. Pat. No. 5,290,471) disclose compositions with C8 to C22 acyl isethionates, synthetics, and free fatty acid, preferably C16 or higher. The alkanolamide and/or alkylamineoxide surfactant crystal modifiers of the subject invention are not disclosed; nor is a process to use both these modifiers and second ingredient specifically together to provide long term stabilization system for the acyl isethionates.
U.S. Pat. No. 5,952,286 and U.S. Pat. No. 6,077,816, both to Puvvada, disclose liquid cleansing compositions which may contain acyl isethionates and which comprise soluble, lamellar phase inducing structurant (e.g., branched fatty acid). While amides may be optionally used in a long recitation of optional ingredients, there is no teaching or disclosure that they need be used; that they must be used in combination with a alkanolamide and/or alkylamineoxide to provide acyl isethionate stabilization system; let alone that the ingredients of the stabilization system must be used in certain minimal amounts.
Applicants filed in December 2006 three cases relating to liquid compositions with crystal modifier systems similar to those of the subject invention. It would not have been predictable in any of these applications, however, that the modifier could be used or would function in compositions where the fatty acyl isethionate surfactant product comprises 60% or more of the surfactant system by forming viscous surfactant liquid crystals upon the dissolution of fatty acyl isethionate/fatty acid crystals at elevated temperatures (40° C. or above).
None of the references, alone or together, teach or suggest compositions comprising fatty acyl isethionate surfactant product as the primary surfactant at a level of at least 60 wt %, preferably 70 wt % of total fatty acyl isethionate surfactant product and other synthetic surfactants in the liquid composition where acyl isethionate/fatty acid crystals formed at room temperature are partially converted to viscous surfactant liquid crystals at elevated temperatures (40 C or above) upon the dissolution of the acyl isethionate/fatty acid crystals using specific surfactant crystal modifier system/stabilization system comprising a combination of alkanolamide and/or alkylamine oxide together with an ingredient selected from the group consisting of ammonium salt, organic amine, hydrocarbon oils, fatty alcohols, fatty acids and mixtures thereof in order to provide acyl isethionate containing liquids, regardless of the fatty acid content or fatty acid chain length of the acyl isethionates surfactant, free fatty acid or fatty acid soap; the compositions formed have a product viscosity less sensitive to temperature, and are stable at elevated temperature storage conditions.